If we don't cease to exist we could do that in a lot less time than 50k years. We could do it, and a lot more, in under 2k years.

Assumption: we can indefinitely keep producing solar panels at a rate at least as high as current production. I will call the amount of solar panels currently produced in one year an "arseload" of solar panels.

If we produced 1600 arseloads of solar panels (which would take 1600 years at the current rate of production) and used those to build solar farms in the 5 largest tropical deserts, and used the power from those to power direct air carbon capture operating at the efficiency of current direct air carbon capture (DAC) technology they would be removing enough carbon at a rate that would reduce the atmospheric CO2 levels from 450 ppm to 280 ppm (pre-industrial levels) in 6 years.

If the captured carbon was stored as graphite and spread out evenly under that 1600 arseloads of solar panels (which seems like a convenient place for it) it would be a layer roughly 1 cm deep.

Note that at around 180 arseloads of solar panels powering DAC we'd be removing CO2 fast enough to be removing about 10% more each year than we currently omit so even if we can't manage to reduce fossil fuels if we can at least finally stop their growth we can start having CO2 reduction in a couple hundred years.

I've not done the math to figure out when a program of adding an arseload of solar panel powered DAC to tropical deserts every year would actually get us back to pre-industrial levels. It's somewhere between 200 and 2000 years, but I'll leave it to others to figure out where in that range it would actually happen.

This is satire right?

However, there are still two very solid arguments for capture, even if it has greater costs.

First, even if we somehow make emissions go to zero next Monday and forever after, the CO2 already baked into the atmosphere will still cause massive warming for centuries, and this will cause massive ecological disuption. Only removing the carbon (and/or implementing sun-blocking technologies) will allow a fast enough reset to pre-industrial levels and avoid such damage.

Second, it is extremely unlikely that we could make emissions go to zero in anything like the required timeframe. Even if somehow 100% of the people and politicians became convinced and decided to start next Monday, it would be decades before we approached zero emissions. Replacing all the fossil-fuel technology will not be instant. Thus, again, capture and sun-blocking tech has a definite role in rapidly repairing the damage.

What about politically effective? You can start removing CO2 from the air without coordinating your effort with all the industrial powers of the world.

This is an invalid argument, in a world where China and the US are quickly becoming sworn enemies unlikely to agree on anything?

We're definitely not at that point, or anywhere near it, but it exists.

First, it was not the original energy expenditure that is the problem. The problem is that the CO2 CHANGES the solar energy exchange equation, by allowing ~the same amount of solar energy to the earth's surface, but REDUCING the earth's ability radiate that energy back to space. That newly captured energy VASTLY EXCEEDS the original energy that went into adding the CO2 to the atmosphere. That original energy spent has almost zero impact on climate change.

Next, capture requires none of the things you say.

— Carbon capture can be done by 'farming' high-uptake organisms, which has extreme leverage for energy expended. Examples include iron-seeding of water to make algae blooms, planting high uptake trees, etc.

— Carbon capture can be done by accelerating natural chemical processes, e.g., exposing rocks that react with water and CO@, or crushing those rocks and spreading them on fields (iirc, Google just contracted with a company doing exactly that)

— Carbon capture can be done by enzyme-driven processes that make the desired reactions happen with minimal artificial energy input

— Even if you want to use a chemistry that requires direct energy input, there is zero requirement to recover the original highly complex and energy-dense molecules previously used for fuel, it only needs to make a compound that can be captured. Still requires less energy than original used.

— Even if you insist on producing new molecules as energy-dense as the originals, there is vastly more energy available via non-CO2-outputting sources, such as solar, wind, etc. which often produce surpluses. Again, the energy of the process has almost zero to do with promoting climate change.

So, NO, it neither a bad joke, a process that requires breaking laws of physics, at fantasy, or a scam.

Specifically, in this case, the standard enthalpy of formation of carbon dioxide is -393.5 kilojoules per mole (that's the energy you get when you burn coal). If you burn coal in a sealed 1-bar chamber to drive a heat engine (such as a steam turbine), and pump the exhaust gases through a passively-air-cooled 1-bar heat exchanger to cool them back down to room temperature, you have obtained those 394kJ/mol thermal, about 138kJ/mol electric, for only the cost of blowing the gas around, without releasing any carbon dioxide into the atmosphere. Blowing the gas around with blowers takes typically about three orders of magnitude less energy than the heat energy the gas carries, though this depends on things like gas temperature and duct length, diameter, and smoothness. So physics is no bar (heh!) to getting from the coal-and-atmospheric-oxygen state into the electricity-and-captured-carbon-dioxide state.

There is some necessary energy cost involved in atmospheric carbon dioxide capture, because the air is only 400 ppm carbon dioxide and 99.96% other things, so there is an entropic cost to unmixing it. That entropic cost is not where you get the energy from burning it; the mixing happens above your smokestack where you can't extract any energy released and, as demonstrated above, can be avoided entirely. I don't understand thermodynamics well enough to calculate the thermodynamically necessary energy to reverse that entropy, but my understanding is that even at 400ppm it is orders of magnitude lower than the fuel's heating value.

Recompressing the carbon dioxide to liquid form requires about as much energy as you got in mechanical form out of the turbine; carbon dioxide liquefies at room temperature at 60 bar, liberating its enthalpy of vaporization of 16.7 kilojoules per mole, 4.2% of the enthalpy of formation. 59 bar is 5.9 kJ/l, and at room temperature and 1 bar an ideal gas occupies 24.4 l/mol, so you need to put about 140kJ/mol into compression. But as I understand it (and correct me if I'm wrong) almost all of that energy comes back out as heat. In practice, atmospheric carbon capture systems use absorbents or adsorbents such as calcium oxide, zeolites, or ethanolamine solutions to avoid this complicated and inefficient compression step. They use a substantial amount of energy to regenerate the sorbents, but, as I understand it, much less than burning the fuel generates.

For example, https://cobblab.eas.gatech.edu/energy/Readings/rochelle2009.... (DOI: 10.1126/science.1176731) says that a monoethanolamine scrubber used for flue-gas treatment at a 450-megawatt power plant in the year 02006 used 0.37 megawatt hours per ton of CO₂ removed. Assuming they mean metric tonnes, that's 1.332 gigajoules per 22700 moles of CO₂, which works out to 59kJ/mol, which is 43% of the energy obtained from burning the carbon. (Although amine scrubbers have been used for capturing CO₂ from flue gas at a number of power plants since the 01980s, I'm unclear on whether this 59kJ/mol number represents measurements from an actually deployed system or the projected performance of a proposed design.)

You could argue that it's easier to remove CO₂ from power-plant flue gas where it's fairly concentrated (12% rather than 0.04%), but in fact sorbents like monoethanolamine and triethanolamine are also quite effective at removing CO₂ from breathable air in environments such as submarines and space stations. At room temperature, their vapor pressure of CO₂ is quite low indeed, so it's mostly just a question of needing to expose the sorbent solution to air over a longer period of time. It doesn't result in requiring a proportional increase in the energy consumption of the process.

A recent open-access survey of the direct-air-capture problem is https://pubs.rsc.org/en/content/articlepdf/2022/ee/d1ee03523... (doi 10.1039/d1ee03523a). (However, note that that's still from November 02021, at which point photovoltaic panels still cost three times as much as they do now, so its calculations of energy costs are inflated by at least a factor of three.)

So, no, the laws of physics don't require that removing CO₂ will require even as much energy as what went into adding it to the atmosphere, much less "massively more energy", as you claim.

Even if they did, though, that wouldn't make atmospheric carbon capture impractical or a scam. Burning methane (natural gas) yields 55.6 MJ/kg (https://en.wikipedia.org/wiki/Energy_density#Chemical_reacti...) which works out to 892kJ/mol, but each mole of methane only produces one mole of carbon. The other 892 - 394 = 498kJ/mol (HHV) comes from burning the hydrogen (water's enthalpy of formation is -285.83kJ/mol, and methane's is -74.6kJ/mol, so we get 497.1 kJ/mol extra after the rounding errors). So even if we had to pay back all of that 286kJ/mol from the carbon to stuff it back into a bottle, we'd still have 56% of the energy we got from burning the natural gas left over.

And, of course, photovoltaics and wind provide abundant energy we can use for atmospheric carbon capture without releasing any more carbon dioxide, and nowadays they do it far more cheaply than fossil-fuel power plants ever did.

There are also schemes for atmospheric carbon dioxide capture with biological photosynthesis, which I think are probably not feasible at the required scale due to the required area, and with enhanced weathering by pulverizing olivines, which are probably feasible but strike me as risky. In the olivine case, the energy required to extract the gas from the atmosphere was provided billions of years ago by the heat of the earth driving carbon dioxide and other volatiles out of the mantle, so we don't have to care how big it is.

The reason "every single proposal for CO2 removal has failed" is (1) most of them are pretty energy-intensive, and until five years ago, energy was expensive (and cheap energy still hasn't reached most places); and (2) there's no clear way to make money at CO2 removal at current carbon credit prices, which are in part because the carbon credit market is pretty corrupt but also because at this point there's still a lot of low-hanging fruit in the emissions-reduction sector.

The reaction of CO2 with silicate rocks that pulls CO2 out of the atmosphere naturally (and is why the Earth is not like Venus with 90 bar of CO2 in the atmosphere) is exothermic. So, the energy needed is not just not large, it could even be negative.

Reality has changed significantly since 02014, though. Konigstein and Fork's article is framed by and based on Google's 02011 failure to make "RE<C", renewable energy cheaper than coal. But renewable energy is (and I'm aware that I'm arguably stating the obvious here) now much cheaper than coal and continues to decline in cost. (It has been much cheaper than coal for several years now in some places, though only in small parts of China, Northern Europe, and North America.) This violates the assumptions the article relies on; renewable energy is already vastly exceeding what the researchers considered "the most extraordinary success possible".

In 02014 PV panels cost 0.55 euros per peak watt (data from http://www.solarserver.com/service/pvx-spot-market-price-ind... visited 2016-02-18) and now the low-cost ones cost 0.060 euros per peak watt, and the mainstream ones (with warranties) cost 0.100 euros per peak watt. This implies the availability of intermittent energy for carbon-capture schemes at about an order of magnitude lower cost than was feasible when the paper came out; that changes the economics of carbon capture in favor of systems with lower capital equipment and materials costs and higher energy intensity

(The price in the US is still much higher due to a series of punitive tariffs against Chinese solar panels, presumably as a subsidy to the US's faltering fossil-fuel industries, but it's important to use unsubsidized prices for these calculations.)

Solar panel manufacturing can probably scale up to build many times current world marketed energy production, but only a small fraction of current world marketed energy production would be needed for atmospheric carbon capture, even with lower-energy-efficiency methods.

I previously did a ballpark number on atmospheric carbon capture via lime burning, but can't find it at the moment. But, essentially, the idea is that, if energy is free, you use it to heat limestone up to 900 degrees in a low-pressure sealed retort, driving the carbon dioxide out of it and making lime cement. You capture the nearly pure carbon dioxide thus produced, passively cool it, liquefy it, and inject it down gas wells into olivine rock formations, where it is permanently sequestered by serpentinization. Then you use the lime cement for building, at which point it reabsorbs an equivalent amount of CO2 from the air.

Due to the disruptive innovation in PV, no "disruptive technologies in carbon storage" are needed, just the Paleolithic technology of lime burning and the well-proven technologies of drilling gas wells.

The feedstocks and capital investment required for this approach are relatively small, a few times larger than the existing global cement industry, which is only 400 billion dollars a year, 0.4% of the global economy. What has made it uneconomical historically is the cost of energy, which is now in free fall thanks to solar panel manufacturers in the People's Republic of China achieving what Google failed at.

(This is not the only possible way to use superabundant solar energy to capture carbon cheaply; for example, the chloralkali process produces NaOH from salt water, and by reacting a slight excess of NaOH with magnesium chloride brine derived from seawater desalination, you get a magnesium analogue of the soda-lime used in scuba rebreathers, which rapidly absorbs carbon dioxide from air and sequesters it permanently as hydromagnesite.)

Consequently the majority of new power generation capacity in China is now solar and wind, even after correcting for their lower capacity factors, and China's carbon emissions seem to have peaked in February and are now in decline. China is especially important here not just because they consume the majority of the world's coal and a quarter of its marketed energy (5.5 terawatts out of 20) but because they produce 80% of the world's solar panels and because, unlike any other energy-intensive country, they are rapidly expanding their energy infrastructure.

The Google paper from 02014 says, "With exponential growth in deployment, businesses could be replacing 30 gigawatts of installed capacity annually by 2040." China's PV generation capacity stands at about 800 gigawatts (ac, peak) and is growing about 3% per month, which is to say, 25 gigawatts per month. What the paper's authors dared to hope might be happening yearly 26 years from now is happening monthly, already. (Except that it's mostly not replacing fossil-fuel generation yet, but augmenting it, because China's energy consumption is growing rapidly.)

The other articles you cite are similarly premised on the now-obsolete assumption that energy will remain expensive and therefore require energy-efficient carbon capture processes. Harvey is quoted as saying, "You'd have to build way more renewables than we need to stop burning fossil fuels altogether," apparently unaware that this is in fact already happening.

The Potsdam paper (https://www.nature.com/articles/nclimate2729) isn't about global warming at all except incidentally; it's about what happens with ocean acidification under the assumption that atmospheric carbon dioxide levels continue rising for 200 years to five times their current level. It doesn't investigate the feasibility of carbon capture, but rather what happens if atmospheric carbon dioxide rises to deadly levels far in excess of current levels and stays there for centuries before carbon capture is attempted.

There's still the question of what system of incentives would motivate spending on the order of a trillion dollars a year on carbon capture and sequestration, since nobody is buying the serpentine at the bottom of the gas injection wells, and the market price of synthetic hydromagnesite is likely to be minimal. Since it's only about 1% of world GDP, it's plausible that international diplomacy could find a solution, as with nuclear weapons reduction and the ozone hole.

But it might turn out not to be necessary; it's plausible that abundant energy will make carbon-neutral extraction of lime from seawater a cheaper way of making cement, including portland cement, than the conventional approach hard-rock mining. Then the cement will absorb carbon dioxide from the air as it cures, though less than lime cement. And it's plausible that it will make carbon dioxide extracted from air a cheaper source of plastic feedstocks than increasingly scarce coal or oil. Perhaps 30 or 100 years from now the pressing environmental problem will be how to halt the depletion of the atmospheric carbon reserves necessary for plant life.

Predicting what will happen is much more difficult than calculating what can happen, but we seem to be on a good path, with atmospheric carbon capture becoming feasible at the necessary terraforming scale within decades rather than centuries.

No. I am telling you that there is no way we can solve it. Doing so requires violating the laws of physics and science in general. That's what does not make sense.

What is clearer proof of the fallacy than knowing precisely how our planet behaves without humanity on it?

We know this. Accurately.

It takes 50K to 100K years for a 100 ppm change in atmospheric CO2.

Nothing. Absolutely nothing we do can improve on this rate of change. I've seen politicians claim we can fix it in 20 to 50 years. Does anyone challenge this nonsense when uttered? No, of course not.

They are claiming we can accelerate a planetary scale problem by a factor of ONE THOUSAND or more and nobody bothers to ask "How?" or "Where is the energy going to come from?" or "How much additional pollution and damage will the proposed process generate?" or "Are you insane?".

We desperately need to start talking about reality and leave these fantasies behind.

> We are not [making a difference]. And we cannot. (...) Same with this ridiculous fantasy of being able to affect climate change at any level. I don't care if the discussion is about keeping it as it is today or reversing it. This is is irrelevant. The entire idea is a fantasy.

But in a comment above you said:

> Humanity burned fossil fuels with incredible energy content per cubic meter. Massive, unthinkable amounts.

> This is how we caused change.

I think the person you are replying to is merely saying in their comment (which you are apparently arguing against) that humanity is currently causing CO₂ buildup and climate change by continuing to burn fossil fuels. It sounds like you don't disagree with what they intended to express, but with some other interpretation. For example, perhaps you are saying that preventing the continued burning of fossil fuels is politically infeasible for some person or group, perhaps collectively the readers of HN?

There are two problems there: ⓐ the collectively suicidal course of action of humanity, of continuing to burn more and more fossil fuels without sequestering the resulting CO₂, and ⓑ the relative powerlessness of that person or group, who hypothetically would be more rational and/or altruistic, therefore choosing a better course of action that would engender a happier future for humanity, even if that meant degrowth. Or have I misunderstood you?

With regard to point ⓑ, I'm not sure what to say. But with regard to point ⓐ, as I explained in https://news.ycombinator.com/item?id=42424292, we're already off that path, even if whatever group of people you're talking about collectively lacks the autonomy to get us back on it.